Composite structure of metal and concrete



April 20, 1954 L. cor-'F 2,675,695

COMPOSITE STRUCTURE OF METAL AND CONCRETE Filed June lO, 1950 2Sheets-Sheet l INVENTOR. [0 COff' www April 20, 1954 1 QOFF 2,675,695

COMPOSITE STRUCTURE OF' METAL AND CONCRETE Filed June 10, 1950 2Sheets-Sheet 2 INVENToR. LEO COFF Patented Apr. Z0, 1954 UNITED STATESPATENT OFFICE COMPOSITE STRUCTURE 0F METAL AND CGNCRETE 3 Claims.

The present invention relates to composite structures of metal andconcrete, the application being a continuation-in-part of my co-pendingapplication Ser. No. 649,010, filed February 2G, 1946, now Patent No.2,510,958, issued June 13, 1950.

In that application I have disclosed means in the `form of a temporaryor permanent reaction member for absorbing the stresses of a tensionedcable or other prestressing member, arranged to impart an upward camberto a metal shape, during the time necessary for the hardening of aconcrete layer which is supported on the metal shape and to which thestress of the cable is subsequently transferred, the concrete and themetal thereafter co-operating as a unitary7 structure in the support ofthe live load applied thereto.

By way of extending the principles described in said application, and ofadvantageously utilizing certain features suggested but not claimedtherein, it is now proposed to employ a permanent reaction member forthe purpose of substantially entirely absorbing the stresses due to deadload, transmission of these stresses to the metal shape being preventedby providing for relative movement between the reaction member and themetal shape until after the concrete has been applied, whereupon theconcrete layer, the metal shape and the reaction member are effectivelybonded together to form the unitary structure desired. Thus, my presentinvention has for its principal object the provision of a compositemetal and concrete structure whose deiiection under dead load will besubstantially nil yet which can be erected without excessivelongitudinal compression of its metal shape, whereby any danger oibuckling of this shape will be obviated.

A still further extension of the principles referred to leads to astructure wherein the' concrete slab itself, or some portion thereof,serves as the reaction member, the essential requirement again beingthat effective consolidation oi the slab and the metal shape be deferreduntil after the prestressing for dead load has been completed.

The invention will be described with reference to the accompanyingdrawing in which:

Fig. 1 is a sectional View, on the line l-i of Fig. 2, or a structuresimilar to that shown in Fig. e is a view similar to Fig. 2 but with theconcrete layer omitted, the structure being similar to that of Fig. 3but comprising a reaction member of modied form;

Fig. 5 is a fragmentary top plan View of a structure representinganother embodiment of the invention;

Fig. 6 is a section on the line 6-6 of Fig. 5;

Fig. 7 is a View similar to Fig. 1, showing a modified structureresembling that of Figs. 5 and 8; and

Fig. S is a section similar' to Fig. 2, showing yet a furthermodification of the structures illustrated in Figs. 5, 6 and 7.

Referring iirst to Figs. 1 and 2, there is shown an arched layer or slabI i supported by a plurality of parallel, longitudinally extending steelbeams i, the ends of these beams resting on spaced supports S (only oneshown) The layer i i is partially broken away in Fig. l to expose areaction member in the form of a row of pre-cast blocks 2li extendingalong the beam or girder l. Side plates 25, welded or otherwise securedto the underside of beam l, are provided at spaced locations to formanchorages for pins 6 which are underslung by a pair oi cables 1, thethreaded terminals l5 of these cables being engaged by nuts l1 whichbear upon anchor plates l5. Ther anchor plates l5 bear, in turn, uponthe end faces of the outermost blocks 24 and the tensioning oi thecables l will thus keep the row of blocks in compression. It will beseen that these outermost blocks are suitably bored or channeled, asindicated at i 9, to enable the unhindered passage ci' cables 1 whichalso traverse the upper ilange of the beam l by way of suitable slots(not shown). It will be readily understood that these slots, as well asthe channels I9, must afford sufficient clearance around the cables 'lto enable their displacement in planes parallel to the axis of beam lwithout the development of objectionable shear stresses in these cables.

Before the slab H is poured, the only positive connection between any ofthe blocks 24 and the metal structure is provided by the engagement ofcables i with pins 6 and by the pins 26. The latter pins pass throughcertain of the blocks 24 and engage slots 27 provided in the side platesIii. The slots are sufhciently elongated to enable relative movementbetween the blocks and the steel beam i when these blocks are placed incompression by tensioning of the cables 1 preparatory to the applicationof the dead load, as well as after the slab I! has `been poured butbeforeV it has hardened. No substantial compression will,

.place.

therefore, be communicated from the blocks to the steel so that anydanger of buckling of the shape I will be obviated.

The blocks 2d are preferably scored or indented, e. g. as indicated at22, to aiTord interlocking engagement between the precast and the pouredconcrete section and to enlarge the contact surface therebetween overwhich bonding is to take The poured concrete also envelops the sideplates 25 and penetrates the slots 2'I thereof so that, once the layerII has hardened, relative movement between the row of blocks 24 and thesteel shape I will no longer be possible. Accordingly, any furthertensioning of the cables 'I (due, for example, to the application oflive load to the structure) will be borne jointly by the metal and theconcrete, the structure then functioning substantially as a monolithicwhole.

If it is desirable to delay tensioning of the cables I not only forlive'load but also for dead load until after the slab has hardened, e.g. in order to prevent buckling of the row of blocks 2.4i, then theimparting of any substantial compression to the steel shape I at thetime of prestressing for dead load can be avoided by providing cavities28 about the side plates 25, these cavities being lled with grout aftercompletion of such prestressing.

Fig. 3 shows a steel beam Ia supporting a flat slab IIa. The upperflange of the beam has bolted thereto a plurality of brackets Staslidably supporting a pipe 2da which represents the reaction member. inthe finished structure the reaction member is imbedded in the concrete.Bearing endwise upon the pipe 24a are anchor plates Ita to which aresecured the threaded terminals I6a of cables la by means of nuts I'Ia.The pipe 24a is shown recessed at 22a to insure intimateand interlockingcontact with the concrete subsequently poured thereover.

The reaction member (pipe 2da) is again free to move relative to theshape Ia until the slab IIa is in place and has hardened around thebrackets 35a and pipe Ella. The hardening of the slab thus immobilizesthe pipe with respect to the concrete and the steel. As before,tensioning of the cables prior to and after application of the dead load(but before hardening of the concrete) places only the pipe incompression. Buckling of the pipe is prevented by the brackets 35a.After the concrete has hardened, the compressive strength of the pipecontributes only to a minor extent to the support of the load.

lf the weight of the dead load is such that the combined steel sectionic, 2da is in danger of buckling before the hardening of the slab IIa,it may be necessary to employ temporary supports at intermediate-pointsof the structure, to be removed after the concrete has set, and to delayuntil such time the tensioning of the cables la. In this event, too, thesteel of the shape Ia should be subjected to little if any compressionin the absence of live load, hence it will be necessary to allow forrelative movement between the slab and the shape and to provide meansfor only thereafter solidifying the structure by rigidly coupling thetwo sections together. This may be done in simple manner by providingslots 27a in the upper ange of the beam ic through which pass the bolts26a holding the brackets 35a onto the flange. After the slab ila hasbecome strong enough to take compression, the cables 'la are tensionedwith the nuts of bolts 25a loosened to enable longitudinal displacementof the brackets 35a, pipe 24a and slab Ila relative to the beam la.Subsequently, the nuts of the bolts 26a. are tightened to produce acondition identical with that previously described. It may be desirableto defer tightening of these nuts until after shrinkage and plastic flowhave reduced the layer or slab I Ia to its ultimate size and after thecables 'la have been retensioned to compensate for this reduction insize. It will, of course, be necessary to provide suitable means forpreventing the entrance of concrete into the slots 27a in order tomaintain relative mobility between the slab iid and the shape Ia; thiscan be done, for example, by the formation of cavities around theseslots substantially in the manner described in connection with Figs. 1and 2.

A variety of elongated metal reaction members may replace the pipe 24ashown in Fig. 3. Fig. 4 shows an I-beam Zlib supported on and extendinglongitudinally of the main beam or girder ib, the two shapes beingjoined together by means of bolts 26h which, however, permitlongitudinal relative movement thereof by passing through longitudinalslots in the flange of either or both beams, in the manner illustratedat 27a in Fig. S. By providing portions 6b of inverted U-shape in thepins 5b, lateral abutments are provided for the cables Tb which, asexplained in my cri-pending application Ser. No. 789,704, filed Decemberfi, 1947, now Patent No. 2,590,685, issued March 25, 1952, preventsbuckling of the shape ib due to tensioning of the cables, thearrangement being similar to that shown in Fig. 2 of my (zo-pendingapplication Ser. No. 57,179, iiled October 29, 1948. By reason of thepresence of the bolts 2th the buckling strength or" the main beam Ibwill be eectively added to that of the auxiliary shape 24h, so that thedanger of buckling due to prostressing for dead load may be readilyaverted by suitably choosing the number and spacing of the pins 6b.

Figs. 5 and `o show how the slab itself, rather than a reaction memberimbedded therein, may be made to absorb the stresses due to dead. loadwithout communicating any material portion ci these stresses to thesupporting shape or shapes, this method being applicable wherever thedead weight of the slab is so low as not unduly to deflect the beamsbefore the cables are tensioned, or where it is convenient to providetemporary intermediate shoring means. Furthermore, the invention in sucha case enables the slab to be composed, in its entirety or for its majorpart, of precast elements which by the action of the Vdead-load stressesthemselves are constrained to act as a unit. These precast elements areshown at IIc and are of generally rectangular configuration, each suchelements spanning a pair of adjacent longitudinal beams ic only two ofwhich are shown. The elements lic abut one another in longitudinaldirection while being spaced in transverse direction, thereby forminglongitudinal channels above the webs of the beams ic which channels areultimately filled with grout as indicated at 25e. Thus the finished slabconsists of the elements I ic and of the groutings 2do.'

Projecting sideways from each of the elements I I c are the ends ofreinforcing rods ric are bent around longitudinally'extending rods 2de,each of the latter rods being thereby supported in one oftheaforementioned channels in alignment with the web of the respective beamic and spaced from the upper flange thereof. Stirrups 35o straddle therods 2&0 and their threaded extremities, engaged by nuts Zc, passthrough longitudinal slots 21e provided in the upper ange of beam Ic.Thus it will be seen that the slab, completed when the grouting 28o inthe longitudinal channels has been hardened, will retain a certainmobility relative to the beams Ic until after the nuts 25o have beentightened, this operation being deferred until after the cables 1c havebeen stressed against the slab to balance the structure for dead load.The tension of these cables operates at the same time to stress thelongitudinally adjacent elements I Ic together for concerted action, aneffect which may be enhanced by form-tting the adjoining edges together,e. g. in the interlocking manner indicated at I Ic.

The arrangement shown in Fig. 7 diiers from that of Figs. 5 and 6 by theuse of hollow precast elements I Id in lieu of the solid slab portions IIc. These hollow elements I Id have the shape of inverted pans, formingcavities bounded by side walls IId and end walls Ild, which, by virtueof their reduced weight, may be higher than the slab portions I Ic, thisin turn enabling the anchor plates d to be raised above the level oftheir counterparts |50, thereby increasing the upwardly acting componentof the tension in the cables 1d.

Fig. 8 shows how, in a structure comprising two longitudinal beams Ie,each pre-cast slab portion IIe may laterally extend, cantilever fashion,beyond these beams while being of double T-bearn configuration by virtueof having two longitudinally extending ribs I Ie' respectively alignedwith these beams, a central cavity and a pair of lateral recesses beingdened by these ribs and by end walls I Ie". Stirrups 35e engagelongitudinal reinforcing rods 24e extending within the ribs IIe', theentire arrangement being structurally similar and functionallyequivalent to that of Figs. 5, 6 and 7 (after the hardening of thegrouting separating laterally adjacent elements IIc or I Id).

It may be mentioned that some means is preferably provided for breakingthe bond between the vertical legs of the stirrups 35o (Figs. 5, 6), 35d(Fig. 7) or 35e (Fig. 8) and the surrounding slabs, as by asphalting orotherwise coating these legs, so that tensioning thereof by thetightening of the associated nuts will be communicated to the rods 24e,24d or 24e, respectively, and thereby to the entire slab, rather thanjust to the concrete in the immediate neighborhood of these stirrups.This Will force the slab into frictional contact with the supportingflanges along practically the whole area of the latter, so that thestirrups will be relieved from bearing the entire shear due to thetendency of the slab to shift under live load relative to the steelshapes.

The embodiments specifically described hereinabove have been givenmerely by way of illustration and not as a limitation upon the scope ofthe invention. Thus it will be understood that a single elongated,precast member may be used in lieu of the aligned blocks 2li, and that alarge variety of means well known per se may be used for anchoring thisor some other reaction member to the composite structure at theopportune moment. It may also be mentioned that relative mobilitybetween the metal shape, on the one hand, and the reaction member and/orthe concrete layer, on the other hand, may be enhanced through theinterposition of an anti-friction layer, e. g. of the character setforth in my aforementioned Patent No. 2,590,685.

I claim:

1. A composite structure comprising an elongated metal shape having asubstantially flat, horizontal bearing surface, a concrete layer restingon said surface, an elongated, compressionresistant element imbedded insaid layer and extending along said surface, at least one iiexible,elastic tie member anchored to the ends of said element and extendingunderneath said surface, tension means maintaining said tie member understress, bracing means supporting at least one intermediate point of saidshape on said tie member, connecting means securing said element to saidshape, and means including said layer preventing relative displacementbetween said element and said shape.

2. A structure according to claim 1 wherein said element comprises abody of precast concrete.

3. A structure according to claim 1 wherein said element comprises ametallic shape.

References Cited in the file 0f this patent UNITED STATES PATENTS NumberName Date 9,172X Witty Oct. 14, 1835 273,922 White Mar. 13, 18831,000,088 Haas Aug. 8, 1911 1,594,505 Frye Aug. 3, 1926 2,101,538 FaberDec. 7, 1937 2,378,584 Schorer June 19, 1945 2,382,139 Cueni Aug. 14,1945 2,449,276 Chalos Sept. 14, 1948 2,510,958 Coif June 13', 1950FOREIGN PATENTS Number Country Date 117,344 Great Britain July 18, 1918464,361 Great Britain Apr. 16, 1937

